Symptoms of a faulty IAC...
Mar 31, 2010, 06:29 PM
#1
Symptoms of a faulty IAC...
A few months ago a problem popped up on my car where when hot starting it would idle at about 3500 rpm for about 10 seconds and then fall to normal idle (1100). This hadn't happened before in the summer months and I figured it was due to the cold weather moving in. Well it's warmer now and the problem is still there. The tune hasn't been touched (Buschur tuned 9/09) and no other mods have been done. I finally got around to pulling the throttle body to inspect the IAC. Everything looks fine, no carbon build up, valve looks ok, although I really don't know what to look for, hence the thread. As I mentioned, this only happens when the car is hot. The longer it sits to cool, the less high it goes in idle on start up. If I start it after one hour after, I'll get 2k rpm idle, 10 minutes, 3500 rpm idle, and so on. Mods are below, if more info is required to nail this down, lmk.
Last edited by black95tt; Mar 31, 2010 at 06:35 PM.
Mar 31, 2010, 06:43 PM
#3
Yeah, i cleaned the throttle plate and surrounding area. When I took the IAC off the throttle body, there was very little carbon build up...like almost none. I was hoping there would be a noticeable problem, but that doesn't seem so.
Mar 31, 2010, 07:28 PM
#6
Unfortunately the IAC always always always "looks" fine, (well unless it's just broken to pieces which I've never seen) however looking at it will not tell you if it's good but you're in luck because it is VERY easy to test the IAC.
1. Unscrew the 3 screws that hold it in and leave it connected to the electrical connector.
2. Have someone else (or you can do this yourself) turn the car to ON but don't crank it.
The little knob on the IAC should slide in and out as it looks for the correct place to dial in for your idle and it makes alot of clicking noises as it slides in and out. It is very easy to hear it. When my idle is off and I'm cruising and drop the clutch as the car almost dies if I listen I can hear the IAC moving to catch the idle. If it doesn't move at all, the IAC is dead. Also make sure to check for the o-ring gasket on the IAC. It is a very unique and specific size/thickness. You can't just find one to swap it in, I've looked and could never get one to fit other than the factory one. If you lost that o-ring that will cause idle issues also. If your IAC is good and the idle is still off check for that o-ring and remove it then lubricate it with some grease (assuming you have it). It's a pretty easy item to diagnosis thank goodness
1. Unscrew the 3 screws that hold it in and leave it connected to the electrical connector.
2. Have someone else (or you can do this yourself) turn the car to ON but don't crank it.
The little knob on the IAC should slide in and out as it looks for the correct place to dial in for your idle and it makes alot of clicking noises as it slides in and out. It is very easy to hear it. When my idle is off and I'm cruising and drop the clutch as the car almost dies if I listen I can hear the IAC moving to catch the idle. If it doesn't move at all, the IAC is dead. Also make sure to check for the o-ring gasket on the IAC. It is a very unique and specific size/thickness. You can't just find one to swap it in, I've looked and could never get one to fit other than the factory one. If you lost that o-ring that will cause idle issues also. If your IAC is good and the idle is still off check for that o-ring and remove it then lubricate it with some grease (assuming you have it). It's a pretty easy item to diagnosis thank goodness
Last edited by 05blue8; Mar 31, 2010 at 07:33 PM.
Mar 31, 2010, 07:48 PM
#7
I had to replace two IACs on my 03 Evo...replaced the oem with a used IAC...then that went out a year later and I replaced that one with another used one....still going strong!
My car would not idle when my IAC went out. I could hold the accelerator and keep the engine running that way.
My car would not idle when my IAC went out. I could hold the accelerator and keep the engine running that way.
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Fish Quintana (Oct 1, 2019)
Apr 21, 2010, 07:46 AM
#11
Evolved Member
On older Mitsu's, and I assume, still on the Evo, the IAC position is not remembered when the engine is shut off. Instead, the IAC is run to the end of it travel at start and then advanced a certain amount to allow the correct amount of air for start.
I had a car where the idle was off at start and the IAC passed all the checks suggested in the manual. So, I lubed it up and replaced it and it work correctly for about a month. After doing this a few times I gave up and bought a new unit.
What I think was happening was that when the IAC was commanded to run all the way to the end of travel, because it was draggy, it didn't get there before commanded to open for start. This has to happen very fast. So, the position was off.
I had a car where the idle was off at start and the IAC passed all the checks suggested in the manual. So, I lubed it up and replaced it and it work correctly for about a month. After doing this a few times I gave up and bought a new unit.
What I think was happening was that when the IAC was commanded to run all the way to the end of travel, because it was draggy, it didn't get there before commanded to open for start. This has to happen very fast. So, the position was off.
Last edited by barneyb; Apr 21, 2010 at 07:49 AM.
Apr 21, 2010, 10:48 AM
#12
On older Mitsu's, and I assume, still on the Evo, the IAC position is not remembered when the engine is shut off. Instead, the IAC is run to the end of it travel at start and then advanced a certain amount to allow the correct amount of air for start.
I had a car where the idle was off at start and the IAC passed all the checks suggested in the manual. So, I lubed it up and replaced it and it work correctly for about a month. After doing this a few times I gave up and bought a new unit.
What I think was happening was that when the IAC was commanded to run all the way to the end of travel, because it was draggy, it didn't get there before commanded to open for start. This has to happen very fast. So, the position was off.
I had a car where the idle was off at start and the IAC passed all the checks suggested in the manual. So, I lubed it up and replaced it and it work correctly for about a month. After doing this a few times I gave up and bought a new unit.
What I think was happening was that when the IAC was commanded to run all the way to the end of travel, because it was draggy, it didn't get there before commanded to open for start. This has to happen very fast. So, the position was off.
Last edited by black95tt; Apr 21, 2010 at 10:51 AM.
Apr 21, 2010, 12:00 PM
#15
I did pull the coolant lines and clean the TB, but was careful to not clean off the special coating (whatever it is). The IAC moves and everything checks out. The car idles fine and drives fine, it's just when I start it back up when it's hot. It idles high as hell for about 5 seconds and then settles in. Starting when cold is no problem.